A common mode of a signal may refer to a direct current (DC) component of a signal. When a signal is transmitted from one electronic component to another electronic component, the common mode must be compensated for, such that the signal does not saturate or otherwise affect operation of the other electronic component. Certain signals may contain a large common mode component relative to a signal component. For example, microphone signals often contain a large common mode and a small signal amplitude. FIG. 1 is a graph illustrating a conventional microphone signal. A signal 102 may be a sinusoidal signal with an amplitude 104. The signal 102 may be offset 106 from a ground voltage. The offset 106 may be larger than the amplitude 104 of the signal 102.
When the signal 102 is transmitted from the microphone to an electronic component for processing, the offset 106 may cause problems in the electronic component. For example, the offset 106 of the signal 102 may be larger than a desired operating range of the electronic component. Electronic components, such as amplifiers or analog-to-digital converters (ADCs), receiving the signal 102 may have little to no sensitivity to the amplitude 104 of the signal because the offset 106 saturates the electronic components.
Conventionally, the offset 106 is adjusted by shifting the signal 102 to a lower voltage. However, this shift in the DC offset, or common mode, of the signal 102 may create audible defects in the shifted signal.
FIG. 2 is a graph illustrating the effect of an instantaneous DC offset shift on an audio signal. A line 202 illustrates a signal with a filtered DC step at time 210. The DC step at time 210 creates a glitch in the output of the signal shown at line 204. The DC step from a first common mode of the microphone to a second common mode of the electronic components allows the electronic components to operate in desired voltage ranges. However, the glitch in the signal due to the DC step is undesirable. For example, when the line 202 represents an audio signal from a microphone and the line 204 represents the processed audio signal, the audio signal has been audible altered from the originally measured audio signal from the microphone.
One conventional solution is the placement of a capacitor acting as a blocking capacitor to remove the DC offset component of the audio signal. However, the capacitor size is large, requiring placement of the capacitor as an external discrete component. This external capacitor prevents complete integration of the integrated circuit. Furthermore, the input impedance to the capacitor should be large enough to create a low frequency pole (e.g., below the lower limit of audible range at 20 Hz) to prevent degradation of the audio signal.
Shortcomings mentioned here are only representative and are included simply to highlight that a need exists for improved integrated circuits, particularly for consumer-level devices. Embodiments described here address certain shortcomings but not necessarily each and every one described here or known in the art.